1. Field of the Invention
The present invention relates to a novel tumor cell growth inhibitor. More particularly, the present invention relates to a novel tumor cell growth inhibitor which can be obtained from the culture supernatant of 3T3 cell-derived cell line and which exhibits an inhibitory activity on the growth of tumor cells.
2. Related Art Statement
Synthetic drugs such as chemotherapeutic agents and immunotherapeutic agents have been widely used as anti-tumor agents, but involve problems that the specificity is low and that side effects are serious. On the other hand, a variety of tumor cell growth inhibitors have been identified in tissue culture cells. It is considered that these inhibitors could be anti-tumor agents having a high specificity and minimized in side effects. As such substances, there are known, for example, interferon, lymphotoxin and tumor necrosis factor (TNF). Recently, reports have been made on a tumor cytotoxic factor which is obtained from human-derived fibroblast (Japanese Patent Application Laid-Open No. 1-148197), and tumor cell growth inhibitory factor which is obtained from human-derived lung cancer cell (Japanese Patent Application Laid-Open No. 1-187094).
On the other hand, some cell growth inhibitors have been also isolated from fibroblastic cell line 3T3 cells established from cells which had been obtained from Swiss mouse fetus. That is, Natraj et al. have reported that a growth factor is obtained from the surface layer of 3T3 cells in the stationary phase [Proc. Natl. Aca. Sci. USA, 75, 6115-6119 (1978)]. Harel et al. also have reported that a growth inhibitor having a molecular weight of 40 kDa is obtained from the culture supernatant of 3T3 cells [J. Cell. Physio]., 119, 101-106 (1984); ibid., 123, 139-143 (1985)]. However, it is known that these growth inhibitors do not show any significant inhibitory activity on tumor cells.